PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See Section 10 and Rule 13)
A METHOD OF MILLING A ROTATING CRANKSHAFT PIN
Applicant: BHARAT FORGE LIMITED
An Indian Company of Mundhwa, Pune – 411036, Maharashtra, India.
THE FOLLOWING SPECIFICATION DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE INVENTION
The present invention relates to a method for machining of eccentric work piece surface, especially a Crankshaft.
More particularly, the present invention relates to methods for machining a crankshaft’smovable or rotating Crank Pin using an elliptical orbital machining/milling.
BACKGROUND OF THE INVENTION
Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
The crankshaft is a vital structural component of the internal combustion engine. It consists of cylindrical shafts i.e. main journals and pins, which converts reciprocating motion into rotary motion. To achieve desired conversion efficiently, narrow tolerance related to deviations in shape, position and dimensions is required on crankshaft pin and main journals. The narrow tolerances are achieved on forged/cast crankshafts by series of roughing and finish machining operations like turning, milling, grinding and superfinishing.
Roughing operationslike eccentric turning, chasing external milling and rotaryor circular orbital internal milling are generally used to remove the excessive material from crankshaft pins.
During the conventionaleccentric turning method, crankshaft is mounted on a lathe/turning center by using special fixtures and then excessive material (machining allowance) from crankshaft pins are removed by a single-point cutting tool. The special fixturesare used to align thecenter/longitudinal axis of crankshaft pin with center axis of the lathe/machine which ensures that the crankshaft rotates around the pin axis. Further, the special fixtures also counterbalance the eccentric crankshaft with suitable weight. The main disadvantage of this type of roughing operation is that the loading condition of the crankshaft on the lathe/turning center needs to be changed for every pin in order to align the axis of pin with lathe/machine center axis.

According to another known method i.e. chasing external milling method, crankshaft is mounted on a horizontal/vertical machining center where crankshaft pin, to be machined, is rotated about a given axis that is parallel to the axis of crankshaft pin. The excessive material (machining allowance)on crankshaft pins is removed using a cutter with inserts mounted on its external periphery. In this method, axis of the milling cutter is perpendicular to the axis of the crankshaft pins. The main disadvantage of this type of roughing operations is multiplenumbers of passes are required to achieve circular cylindrical shape of pin which is time consuming.
Another known method is to machine the crankshaft pins by rotary or circular orbital internal milling method. In this method,the crankshaft is mounted on a special purpose milling center. Next, the crankshaft pin, to be machined, is fixed or rotated about an axis that is parallel to the axis of crankshaft pin. After this, the excessive material (machining allowance) on crankshaft pin is removed by a circular or disc type milling cutter with a number of inserts mounted on the circumference of its inner diameter which acts as a multipoint cutting tool. In this method, the axis of the milling cutter is parallel to the axis of the crankshaft pins. This circular or disc type milling cutter is capable of making heavy depth of cut during cutting. In Rotary or circular orbital internal milling operation, excess material (machining allowance) is removed in single pass of cutter to achieve circular cylindrical shape of pin which takes less time as compared to other two methods, so rotary milling is more relevant and cost effective method for crank pin milling.
The main objective of the roughing machining operation is to ensure large depth of cut and provide uniform stock on diameter for subsequent finishing operation like grinding. Rotary or circularorbital internal milling is cost effective roughing method for crankshaft pin over the eccentric turning and chasing external milling, as it allows heavy depth of cut and has lower cycle time as compared to thesemethods. Rotary or circular orbitalinternal milling or “CIM” generates circular cylindrical shape of the crankshaft pins by a circular orbital movement between the milling cutter and pin circumference.

CIM can be operated using one of thethree different working principles. These working principles are differentiated according to the interpolation method used for definition of the movement path of the horizontal and vertical axis of the milling head. These three working principles are:1. movable or Rotating crankshaft pin (MCP) method; 2. fixed crankshaft pin method and, 3. rotating crankshaft pin and eccentric cutter method.
The CIM method using the MCP principle used in the prior art practice for machining of pin of a crankshaft involved the use of a cutter which rotates along its center and simultaneously slides in a direction perpendicular to its central axis. During the movement of the cutter, the crankshaft pin in contact with the cutter also moves or rotates about the crankshaft’s central axis (207) with throw pitch circle diameter which creates a circular orbital motion between crankshaft pin circumference and milling cutter.
Over the time, the CIM method using the MCP principleproduces high material deformation and high cutting forces due to axis errors in machine parts that is a result of large depth of cut and high contact area between cutter inserts and workpiece surfaces, which further leads to dimensional and geometrical inaccuracies on the crankshaft pin and reduced productivity. These surface inaccuracies further lead to issues like unclean diameter, wheel wear, grinding burns, throw out etc. in the subsequent grinding stage. The conventional method of CIM using MCP has following disadvantages.
1. Quality of miller crankshafts is not consistent and good.
2. Due to axis error in milling machine, the roundness profile of crankshaft pins is not within spec in some of the milled crankshafts. Due to this roundness error, some of these parts get rejected/scrapped. Typically, due to roundness error, the pin diameter becomes elliptical in shape.
3. Due to the axis errors and roundness problems in milled crankshaft, the cutting parameters have to modify or fine-tuned regularly which leads tolower productivity of milling operation.

4. The roundness error in milling output leads to non-uniform stock or machining allowance on diameter for subsequent grinding operation as the shape of pin becomes elliptical instead of circular.
5. The non-uniform machining allowance on the milled crankshaft leads togrinding issues like unclean diameter, uneven wheel wear, grinding burns, throw out and so on.
6. These issues lead to loss of productivity in grinding, increase in cost of process due to frequent change in grinding tool and inconsistent and bad quality products.
Accordingly, it is required to provide a method which can overcome the above stated drawbacks of rotary or circular orbital internal milling (CIM) method using the movable or rotating crankpin (MCP) principle.
OBJECTS OF THE INVENTION
Some of the objects of the present invention, which at least one embodiment herein satisfies, are now disclosed.
It is an object of the present invention to provide an improved elliptical orbital internal milling (EIM) method using the movable or rotating crank pin (MCP) principle to ensure large depth of cut and uniform stock on diameter for subsequent grinding operation.
It is another object of the present invention to eliminate surface and geometric inaccuracies onthe crankshaft pin.
It is stillanother object of the present invention to produce a crankshaft pins with desired fit and tolerance.
It is yet another object of the present invention to provide a flexible interference to user that can handle family of the crankshaft pins with least input.
It is further object of the present invention to provide a flexible interference to user that can easily optimize the product specific parameters for achieving best quality.

Other objects and advantages of the present disclosure will be more apparent from the following description which is not intended to limit the scope of the present disclosure.
BRIEF DESCRIPTION OF DRAWINGS
The accompanying drawings are included to provide further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The drawings are for illustration only, which thus is not a limitation of the present disclosure.
FIG. 1 illustrates an exemplary flow diagram for a method of elliptical orbital internal milling (EIM) using the movable or rotating crankshaft pin (MCP) principle, in accordance with an embodiment of the present disclosure.
FIG. 2illustrates an exemplary diagram of crankshaft loading for a method of elliptical orbital internal milling (EIM)using the movable or rotating crankshaft pin (MCP) principle, in accordance with an embodiment of the present disclosure.
FIG. 3a and 3b illustrates an exemplary cycle of a method of elliptical orbital internal milling (EIM) using the movable or rotating crankshaft pin (MCP) principle, in accordance with an embodiment of the present disclosure.
FIG 4a and 4b illustrates crankshaft pin roundness evaluation plot of rotary or circular orbital internal milling (CIM) using the movable or rotating crank pin (MCP) principleand elliptical orbital internal milling (EIM)using the movable or rotating crank pin (MCP) principle.
SUMMARY OF THE INVENTION
In accordance with the present invention, an EIM method using the MCP principleis disclosed for producing specified form, fit and tolerance on a crankshaft pin. In particular, a mathematical formula for obtaining co-ordinates, in the direction perpendicular to cutter’s center axis, to generate tool path is provided which compensate the ovality produced by the inherent behavior of the machining center. EIM method ensures large depth of cut i.e. high material removal rate with low cost and uniform stock on pin diameter for subsequent grindingoperation.

Further, invention provides flexible interference to user that can handle family of crankshaft pins with least input and easily optimize the product specific parameters for best quality.
In accordance with the presently claimed invention there is provided a method of milling a rotating crankshaft (refer figure 1 and 2), said method comprising the following steps:
- placing a crankshaft (201) having a first end, second end, main
journals (202) and crankshaft pins (203), on a milling machine adapted
for machining of the crankshaft pins,
wherein the milling machine comprises a milling head with an internal milling cutter (208) which surrounds the crankshaft (201),
- holding said crankshaft (201) between the machine centers (204) along
the longitudinal direction (205),
wherein angular position of crankshaft pin is aligned by aligning jaws (209) and the first and second ends of crankshaft are clamped by clamping chucks
(206) mounted along the longitudinal axis (207) of the machine,
- rotating the crankshaft’s pin about crankshaft’s central axis with throw
pitch circle diameter
- circumference milling said crankshaft using the milling machine,
wherein said milling comprises positioning the milling cutter (208)
longitudinally at a pin location, rotating the cutter at a pre-defined RPM along its center and simultaneously sliding in a direction perpendicular to its central axis
(207) to create an elliptical orbital path or motion around the crankshaft pin
circumference, and perform pin circumference milling, wherein during the
movement of the cutter, the crankshaft pin circumference is in engagement with
cutter resulting into rotation about the crankshaft’s central axis (207) with throw
pitch circle diameter (212); and
- unloading the crankshaft from the machine,
wherein, the rotation and simultaneous sliding of the cutter in particular direction corresponds to co-ordinates obtained from a numerical control system. DETAILED DESCRIPTION OF INVENTION

The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
The CIM method using the MCP principle used in the prior art practice for machining of pin of a crankshaft involved the use of a cutter which rotates along its center and simultaneously slides in a direction perpendicular to its central axis. During the movement of the cutter, the crankshaft pin in contact with the cutter also moves or rotates about the crankshaft’s central axis with throw pitch circle diameter which creates a circular orbital motion between crankshaft pin circumference and milling cutter.
Over the time, the CIM method using the MCP principle produces high material deformation and high cutting forces due to axis errors in machine parts that is result of large depth of cut and high contact area between cutter inserts and workpiece surfaces, which further leads to dimensional and geometrical inaccuracies on crankshaft pin and reduced productivity. These surface inaccuracies further leads to issues like unclean diameter, wheel wear, grinding burns, throw out etc. in the subsequent grinding stage. The axis errors in the milling center leads to error in the roundness of the crankshaft pins. This error manifests itself in the form of ellipticalshape of the crankshaft pins. This elliptical shaped pin may lead to rejection at milling stage or in the subsequent grinding stage.
One way to overcome this disadvantage of the conventional CIM using MCP would be to provide a method to compensate for these axis errors. This compensation can be provided in the milling tool motion through the numerical control of the machine. For this, the coordinates of the elliptical path has to be calculated accuratelybased on the axis errors present in the machine and providing it to the NC of the machine.Currently, there is no provision in numerical control

to provide compensation for axis errors and thus, improve the geometrical shape of pin diameter caused by above errors.
Accordingly, in order to eliminate the drawbacks of CIM machining operation, the present invention provides an elliptical orbital internal milling/machining (EIM). In one embodiment, these tool paths are used for milling/machining of crankshaft’s pins in order to offset or compensate the ovality produced by inherent behavior of the machining center.
In accordance with the presently claimed invention there is provided a method of milling a rotating crankshaft (refer figure 1 and 2), said method comprising the following steps:
a) placing a crankshaft (201) having a first end, second end, main
journals (202) and crankshaft pins (203), on a milling machine adapted for
machining of the crankshaft pins,
wherein the milling machine comprises a milling head with an internal milling cutter (208) which surrounds the crankshaft (201),
b) holding said crankshaft (201) between the machine centers (204)
along the longitudinal direction (205),
wherein angular position of crankshaft pin is aligned by aligning jaws (209) and the first and second ends of crankshaft are clamped by clamping chucks
(206) mounted along the longitudinal axis (207) of the machine,
c) rotating the crankshaft’s pin about crankshaft’s central axis with
throw pitch circle diameter
d) circumference milling said crankshaft using the milling machine,
wherein said milling comprises positioning the milling cutter (208)
longitudinally at a pin location, rotating the cutter at a pre-defined RPM along its center and simultaneously sliding in a direction perpendicular to its central axis
(207) to create an elliptical orbital path or motion around the crankshaft pin
circumference, and perform pin circumference milling, wherein during the
movement of the cutter, the crankshaft pin circumference is in engagement with
cutter resulting into rotation about the crankshaft’s central axis (207) with throw
pitch circle diameter (212); and

e) unloading the crankshaft from the machine,
wherein, the rotation and simultaneous sliding of the cutter in particular direction corresponds to co-ordinates obtained from a numerical control system.
In one embodiment, the coordinates are obtained by numerical control system using a mathematical code/equation corresponding to input parameters used in the following mathematical equation:

wherein,
Xn: Milling cutter x-axis coordinates;
a and b : major and minor axis of pin ellipse;
T: throw pitch circle radius;
R: cutter radius;
r: crankshaft pin radius;
0n: pin angular position ; and
a: angular shift of high point.
In one embodiment, the cutter (208) rotates in a clockwise direction w.r.t the axis of the crankshaft (201).
In another embodiment, the cutter (208) rotates in a counter clockwise direction w.r.t the axis of the crankshaft (201).
In one embodiment, the steady rests (210) of the milling machine clamps on the main journal (202) adjacent to the crankshaft pin (203) to be machined.
In one embodiment, the present method is characterized by a synchronized movement of the cutter (208) around crankshaft pin (203) circumference in directions perpendicular to longitudinal axis (207) (x or y direction) which, creates an elliptical orbital path or motion around crankshaft pin (203) circumference.

In one embodiment, the pin (203) circumference is completely milled after completion of one complete rotation of the cutter (208) around the pin (203) circumference.
In one embodiment, the crankshaft (201) and the milling cutter (208) rotates in same direction w.r.t the central axis (207) of the crankshaft (201) and the milling cutter (208).
In one embodiment, the crankshaft (201) and the milling cutter (208) rotates in an opposite direction w.r.t the central axis (207) of the crankshaft (201) and the milling cutter (208).
FIG. 1 illustrates an exemplary flowchart 100 for an elliptical orbital internal milling (EIM) method using the movable or rotating crankshaft pin (MCP) principle, in accordance with an embodiment of the present disclosure.
In one embodiment, the EIM method using the MCP principle comprises: Step 102: Parameters Input, is an input to numerical control system about the design size of crankshaft (i.e. longitudinal positions of Crankshaft Pins, throw pitch circle radius and crankshaft pin radius) and technical requirements (i.e. process parameters, major and minor axis of pin ellipse and angular shift of high point);
Step 104: Crankshaft Loading (200), is providing a crankshaft (201) consisting of main journals (202) and pins (203) and placing said crankshaft (201) on a machine adapted for machining/milling of crankshafts pin(s) (203). The said crankshaft (201) is held between the machine centers (204) along the longitudinal direction (205) and clamped at both ends by clamping chucks (206) mounted on rotational axis or longitudinal axis (207) of machine. Further, angular position of crankshaft pin (203) is aligned by aligning jaws (209). The said machine comprises a milling head with an internal milling cutter (208) which surrounds the crankshaft (201) and is concentric to machine longitudinal axis (207) and steady rests (210) which provides rigidity during crankshaft pin machining/milling. FIG. 2 illustrates an exemplary diagram of crankshaft loading for a method of EIMusing the MCP principle.

Step 106: Data Computation, is calculations of cutter axis data, i.e. coordinates, by numerical control system using mathematical code/equation in accordance to the input parameter in step 102. Step 106 is carried out on the basis of mathematical equation,

wherein,
Xn: Milling cutter X coordinates
a and b : major and minor axis of pin ellipse
T: throw pitch circle radius
R: cutter radius
r: crankshaft pin radius
0n: pin angular position
a: angular shift of high point ,
Step 108: Circumference Milling/Machining, is removal of material from crankshaft pins (203) circumference. In this step, pin (203) is angularly positioned/indexed along the horizontal axis (211) of cutter, milling cutter (208) is positioned longitudinally at pin location and steady rests (210) clamps on main journal adjacent to the crankshaft pin to be machined. Then cutter (208) rotates at predefined RPM along its center and simultaneously slides in one of the directions perpendicular to its central axis (207) as per step 106 output. During the movement of the cutter (208), the crankshaft pin (203) circumference is in contact with the cutter (208) and also moves or rotates about the crankshaft’s central axis (207) with throw pitch circle diameter (212) which creates an elliptical orbital path or motion between crankshaft pin (203) circumference and milling cutter (208). Pin (203) circumference is completely milled after completion of one complete rotation of pin (203) about crankshaft center axis (207). Then steady rest (210) unclamps, cutter (208) return to center position (213) and move longitudinally to next pin (203) position along with steady rests (210). This cycle is repeated until all pins (203) are milled. FIG. 3a is a diagrammatic

representation of the manner in which cutter (208) and crankshaft pin (203) areinitially positioned with respect to each other and Fig. 3b illustrates the manner in which the cutter (208) and crankshaft pin (203) aredisplaced duringpin circumference milling/machining by EIMusing the MCP principle.
Step 110: Crankshaft Unloading, is unloading of crankshaft (201) from machine. After unloading crankshaft pins (203) are inspected as per control plan.
In accordance with the present invention, a mathematical formula for obtaining co-ordinatesin one of the direction perpendicular to cutter’s (208) center axis is developed and providedbelow which further helps in achieving effective EIM machining.

wherein,
Xn: Milling cutter X-axis coordinates
a and b : major and minor axis of pin ellipse
T: throw pitch circle radius
R: cutter radius
r: crankshaft pin radius
Ø' n: pin angular position
a: angular shift of high point
In an aspect, mathematical formula for obtaining co-ordinates of EIM using the MCP principle provides flexible interference to user that can handle family of crankshaft pins (203) with least input.
In another aspect, mathematical formula for obtaining co-ordinates of EIMusing the MCP principleeasily optimizes the product specific parameters i.e. major and minor axis of pin ellipse and angular shift of high point for best quality.
FIG 4a and 4b illustrate crankshaft pin (203) roundness evaluation plots for crankshaft pins (203) machined using CIM using the MCP principle and EIMusing the MCP principle, respectively.

Figure 4a shows that the crankshaft pin under consideration has roundness errors which lead to elliptical shape. Roundness Evaluation Plotsof pins (203) machined using EIM method using the MCP principle shows improved pin roundness profile.
Further, Table 1 shows comparative evaluation of CIM using the MCP principle and EIM using the MCP principle.
Table 1: Comparative evaluation of CIM using the MCP principle and EIM using the MCP principle

Method Roundness (mm)
CIM using the MCP 0.7- 0.95
EIM using the MCP 0.1 – 0.25
The present invention has following advantages.
1. EIM using the MCP principle consistently provides better quality.
2. EIM using the MCP principle shows improved roundness profile of crankshaft pins.
3. EI Musing the MCP principle leads to improved productivity of milling operation by improving cutting parameters.
4. EIM using the MCP principle provides uniform stock on diameter for subsequent grinding operation.
5. EIM using the MCP principle minimizes grinding issues like unclean diameter, uneven wheel wear, grinding burns, throw out and so on.
6. EIM using the MCP principle showsimproved grinding productivity with consistent quality.
The TECHNICAL ADVANCEMENT of the invention lies in the use of basic crankshaft’s parameters in conjunction with mathematical code/equation which have been specifically developed for the machining center to generate tool path for elliptical cutting. These tool paths are then used for the machining

crankshaft’s pinsin order to offset or compensate the ovality produced by inherent behavior of the machining center.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other modifications in the nature of the disclosure or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

WE CLAIM:
1. A method of milling a rotating crankshaft, said method comprising
the following steps:
a) placing a crankshaft (201) having a first end, second end,
main journals (202) and crankshaft pins (203), on a milling machine adapted
for machining of the crankshaft pins (203),
wherein the milling machine comprises a milling head with an internal milling cutter (208) which surrounds the crankshaft (201),
b) holding said crankshaft (201) between the machine centers
(204) along the longitudinal direction (205),
wherein angular position of crankshaft pin (203) is aligned by aligning jaws (209) andthe first and second ends of crankshaft (201) are clamped by clamping chucks (206) mounted along the longitudinal axis (207) of the machine,
c) rotating the crankshaft’s pin (203) about crankshaft’s central axis (207) with throw pitch circle diameter (212)
d) circumference milling said crankshaft (201) using the milling machine,
wherein said milling comprises positioning the milling cutter (208) longitudinally at a crankshaft’s pin (203) location, rotating the cutter (208) at a pre-defined RPM along its central axis (207) and simultaneously sliding in a direction perpendicular to its central axis (207) to create an elliptical orbital path or motion around the crankshaft’s pin (203) circumference, and perform pin circumference milling, wherein during the movement of the cutter (208), the crankshaft pin (203) circumference is in engagement with cutter (208) resulting into rotation about the crankshaft’s central axis (207) with throw pitch circle diameter (212); and
e) unloading the crankshaft (201) from the machine,
wherein, the rotation and simultaneous sliding of the cutter (208) in
particular direction corresponds to co-ordinates obtained from a numerical control system.

2. The method as claimed in claim 1, wherein the method further comprises a step of moving the cutter (208) to the original position (213) post milling the crankshaft pin (203) followed by positioning on another pin (203) location and performing circumference milling.
3. The method as claimed in claim 1, wherein the coordinates are obtained bynumerical control system using a mathematical code/equation corresponding to input parameters used in the following mathematical equation:

wherein,
Xn: Milling cutter x-axis coordinates;
a and b : major and minor axis of pin ellipse;
T: throw pitch circle radius;
R: cutter radius;
r: crankshaft pin radius;
0n: pin angular position ; and
a: angular shift of high point.
4. The method as claimed in claim 1, wherein the cutter (208) rotates in
a clockwise direction w.r.t the axis of the crankshaft (201).
5. The method as claimed in claim 1, wherein the cutter (208) rotates in
a counter clockwise direction w.r.t the axis of the crankshaft (201).

6. The method as claimed in claim 1, wherein the steady rests (210) of the milling machine clamps on the main journal (202) adjacent to the crankshaft pin (203) to be machined.
7. The method as claimed in claim 1, wherein said method is characterized by a synchronized movement of the cutter (208) around crankshaft pin (203) circumference in directions perpendicular to longitudinal axis (207) (x or y direction) which, creates an elliptical orbital path or motion around crankshaft pin (203) circumference.
8. The method as claimed in claim 1, wherein the pin (203) circumference is completely milled after completion of one complete rotation of the cutter (208) around the pin (203) circumference.
9. The method as claimed in claim 1, wherein the crankshaft (201) and the milling cutter (208) rotates in same direction w.r.t the central axis (207) of the crankshaft (201) and the milling cutter (208).
10. The method as claimed in claim 1, wherein the crankshaft (201) and the milling cutter (208) rotates in an opposite direction w.r.t the central axis (207) of the crankshaft (201) and the milling cutter (208).